If the request has the attachment, it won't be attached to the request and the content type will be text/xml.

So the problem is not only on requests with no attachments, but it affects even the requests with attachments. it looks like that the problem is originated by the property mtom-enabled set on the cxf endpoint. one can  check the properties of the endpoint at runtime, and verify that that property is not set anymore.
 
configuration and logs are attached
 
as per logs 'logMessage=REQ_OUT' has 'Content-Type: text/xml;charset=UTF-8'